1. Field of the Invention
The present invention relates to a cross hair assembly.
The present invention relates, more particularly, to a cross hair assembly, usable in an X-ray machine, or similar type apparatus, e.g., an accelerator, for aligning a patient's body with a radiation source.
2. Prior Developments
In certain X-ray machines, or accelerators, usable in the medical field, the patient is positioned in a prone position on a table located below the X-ray source; the X-rays are directed downwardly from an overhead source onto the patient's body.
In order to align the specific area of the patient's body that is being treated, or studied, with the X-ray source, a cross hair assembly and light source are used as an alignment tool. The light source is located on the optical axis of the radiation source directly above the cross hair assembly. With the patient most often in a prone position on the table, the light source is energized to direct a concentrated light beam downwardly through the cross hair assembly onto the patient's body. A cross-shaped shadow is cast on the patient's body, designating the area of the body that will receive the X-rays when the X-ray machine is later turned on. The table, or overhead X-ray source, can then be adjusted, as necessary, to move the cross-shaped shadow to the desired point on the patient's body.
One problem with the existing cross hair assemblies is that the intersection point of the cross hairs may not always be in precise optical alignment with the optical axis of the light source or radiation source. Such misalignment can be related to manufacturing tolerances or day-to-day load forces.
Another disadvantage of the existing cross hair assemblies is that the cross hairs are relatively thick, due to the way in which the cross hairs have to be mounted. Each cross hair comprises a steel wire having a diameter of about 0.050 inch, in order to achieve a reasonably rigid taut wire structure free of bends or wrinkles. The large diameter wire tends to cast a relatively wide shadow line on the patient's body.
A further problem associated with conventional cross hair assemblies is that the individual wires (cross hairs) are not easily replaced. Often, when a cross hair breaks, or otherwise becomes non-operational, the entire cross hair assembly has to be replaced.